416 THE ZOOLOGIST. 



longer, and the second longer still and about as long as the 

 abdomen. The cilia of the second and third setae are strongly 

 developed, but those of the first and fourth are not. The form of 

 the fifth pair of feet is shown in fig. 23, and that of the posterior 

 antennae in fig. 24. The shape of the red eye and the arrange- 

 ment of numerous setae and cilia, not specifically referred to 

 above, can be seen by reference to the various figures. There 

 are two compact, oval, and divergent ovisacs, the angle between 

 their long axes being 60° or more. The colour of the cephalo- 

 thorax is usually brown or yellow, and that of the ovisacs is 

 usually green. From the tip of the cephalothorax to the 

 extremities of the longest tail setae is about 125 mm. or less 

 than ^5-inch, and the cephalothorax is about 0"5 mm. 



The male is smaller, more slender, and, neglecting its swollen 

 anterior antennae, more elegant in form than the female. Its 

 movements are very rapid, and each traverse it makes appears 

 to be slightly zig-zag. Each antenna is swollen and hinged so 

 as to form an "elbow " X and a "wrist" XX, fig. 25, to adapt 

 it for use as a clasper. The capability of movement of the 

 " wrist " is very great, as may be seen by narcotizing the 

 Copepod with eucaine when the terminal part of the antenna is 

 seen repeatedly straightening out and then folding down close 

 on to the rest of the antenna. Fig. 25 was drawn from a male 

 obtained from Parsonage Farm Pool. Only a few of the writings 

 on the Copepoda give a drawing of the antenna of the male 

 C. semdatus. The drawing best known to me is fig. 28, plate x. 

 in vol. 24, second part of the ' Bull, de la Soc. Imp6riale des 

 Naturalistes de Moscou,' 1851, accompanying Sebastian Fischer's 

 account of Copepods from the neighbourhood of Petrograd. 



The length of the antenna, when reflexed, is about equal to 

 that of the first cephalothoracic segment. The total length of 

 the male is 0*85 mm., and of the cephalothorax about 0*38 mm. 



Proceeding to the consideration of the results obtained from 

 the examination of the very large numbers of G. serrulatus from 

 the country of the Chess and Gade, it will be convenient to take 

 in order the following subjects of inquiry : — 



1. The relative numbers of specimens at different times. 



2. The possible conditions favouring the occurrence of large 



numbers of C. serrulatus. 



